In Microsoft's drive to prevent themselves from being embarrassed again by some pimply faced teenager in a third world country, Windows verifies that patches haven't been tampered with. Unfortunately, the combination of huge patch and slow virtual machine means that verifying Visual Studio 2005 SP1 can takes hours. Buried at the bottom of Knowledge Base article 925336 are instructions for shutting off the verification. The section starting with "If the previous steps do not resolve the issue" describes a simple security policy modification that turns off patch verification for administrators. Note that this affects all patches, not just Visual Studio 2005 SP1.